1. Field of the Invention
The present invention relates to a watchdog timer and method for detecting abnormal operations of a computer. The present invention relates also to a computer including the watchdog timer for detecting abnormal operations of the computer.
2. Description of the Related Art
Computers may operate out of control or stop operating as a result of any of various factors, as described in FIG. 9.
Disclosed in Unexamined Japanese Patent Application KOKAI Publication No. S61-62947 is a method, employing a timer, for detecting such abnormal operations of computers and setting the computers back into a normal state.
The timer (watchdog timer) begins operating in accordance with commands of a software program for controlling a computer. The watchdog timer counts pulses of a clock, and the counted value is cleared at predetermined intervals under the control of the software program.
In the case where an abnormal operation occurs in the computer, the counted value exceeds a predetermined limit value instead of being cleared In the case where the counted value exceeds the limit value, the watchdog timer controls the computer to execute a reset process.
However, as described above, the watchdog timer begins operating by the commands of the software program. Hence, the abnormal operation occurring during the activation of the software program can not satisfactorily be detected.
Particularly, in the case where a noise N1 occurs in the power source as shown in FIG. 10, the computer is operated out of control, and the counted value reaches the limit value (C1). Hence, the computer is reset by the watchdog timer, and begins the reset process (C2). However, the noise N1 still remains at the time of beginning the reset process, the computer is again operated out of control. Thus, the software program is not activated, and the watchdog timer docs not operate, either.
Accordingly, the conventional watchdog timer can not detect the abnormal operations occurring in the computer during the activation of the software program.
In the case where the watchdog timer is included in the computer, the computer can not be employed for any apparatuses which do not need the functions of the watchdog timer. In other words, any of those computers each including the watchdog timer can not be used for various purposes.
The contents of Unexamined Japanese Patent Application KOKAI Publication No. S61-62947 are herein incorporated by reference in its entirety.